ARS | Publication request: INJECTION OF INNOCUOUS OILS TO CREATE REACTIVE BARRIERS FOR BIOREMEDIATION: LABORATORY STUDIES

Submitted to: Journal of Contaminant Hydrology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 7, 2005
Publication Date: August 18, 2005
Citation: Hunter, W.J. 2005. Injection of innocuous oils to create reactive barriers for bioremediation: laboratory studies. Journal of Contaminant Hydrology. 80:31-48.

Interpretive Summary: Biobarriers are a promising new technology for removing a number of contaminants form groundwater. Research suggests that nitrate, perchlorate, chlorate, chlorinated solvents (i.e. trichloroethylene or TCE) and metals may be removed from contaminated water by biobarriers containing innocuous vegetable oil. The barrier is positioned downstream of the contaminant plume and contaminants are degraded as the groundwater flow carries them through the barrier. Biobarriers are normally created by digging a trench and backfilling the trench with a mixture of sand, gravel and sawdust. The sand and gravel allow for the movement of water while the sawdust provides a carbon substrate that stimulates microbial activity. Microbial activity in deeper soils and aquifers is usually limited by the availability of carbon. The sawdust provides the carbon stimulating microorganisms to degrade contaminants that serve as microbial electron acceptors. Vegetable oils can also serve as carbon substrates to stimulate microbial activity. Moreover, since vegetable oils are liquids, it may be possible to create biobarriers containing vegetable oils by injecting the oil into the aquifer. However, little is known about the best procedures to use when injecting oil into an aquifer. In this investigation, laboratory column and sand tank studies were used to explore the effect of different injection parameters on the distribution of oil emulsions into water-saturated sand. The parameters investigated included injection pressures of 70, 1400 and 18,000 KPa; injection times of 15, 30, 60 or 120 sec; and the influence of an emulsifier, polyoxyethylenesorbitan monooleate (Tween 80), upon the distribution of the injected oil.

Technical Abstract: In situ groundwater remediation projects, that use continuous injection of soluble substrates, involve the expense of nutrient storage tanks and pumps to deliver the nutrients. Moreover, such projects sometimes fail because of biofouling at or near the injection points. An alternative approach involves remediation by stationary permeable barriers. These reactive biobarriers may be created by the injection of a substrate in the form of a non-aqueous phase liquid, such as innocuous vegetable oils, into the contaminated aquifer. The barrier, positioned downstream of the contaminant plume, would be created at the start of the project by a series of injections that distribute the oil. Microbial activity in deeper soils and aquifers is usually limited by the availability of electron donors. The oil provides the electron donor stimulating microorganisms to degrade contaminants that serve as microbial electron acceptors. Contaminants such as nitrate, perchlorate, or chlorate are degraded as the groundwater flow carries them through the barrier. At present, little is known about the best procedures to use when injecting oil into an aquifer. In this investigation, laboratory column and sand tank studies were used to explore the effect of different injection parameters on the distribution of oil emulsions into water-saturated sand. The parameters investigated included injection pressures of 70, 1400 and 18,000 KPa; injection times of 15, 30, 60 or 120 sec; and the influence of an emulsifier, polyoxyethylenesorbitan monooleate (Tween 80), upon the distribution of the injected oil. The longest injection patterns were achieved at 18,000 KPa. A pattern that was 46 ± 1.8 cm long was produced with an 18,000 KPa injection for 60 sec. Increasing the injection time to 120 sec increased the length of the pattern by only 6.5 %. Tween 80 at concentrations of 0.05% increased the width of the injection patterns but did not increase the length of the pattern. A multi-ported injection probe might be used to create in situ permeable barriers approximately 1 meter wide.